The present invention relates to an acoustic barrier to protect an asset such as a ship that abuts a body of water.
Current world events highlight the need to protect both military and civilian ships that are situated in a harbor environment. Potential threats may originate at the surface of the water or below the surface of the water. In order to protect against underwater threats, a traditional diver sonar (SOund, NAvigation and Ranging) system may employ arrays of transducer elements on a larger structure to achieve many highly directional narrow beams to cover an angular sector of ocean to detect against relevant objects, e.g. divers and swimmer delivery vehicles, while disregarding irrelevant objects, e.g. fish. A traditional diver sonar system typically looks in a horizontal direction and must have significant transmit power to provide detection in a large volume of water over a range of several hundred yards. Such sonar systems are quite expensive, typically in a price range of $500,000 to $1,000,000 and generate high power levels that may be objectionable for environmental reasons. Moreover, to adequately protect a ship in a harbor, several sonar systems may be needed, thus increasing the complexity and the cost. Because a traditional sonar system are large in size, heavy, and require motional stability, the traditional sonar system typically lacks mobile agility and is mounted in a fixed location.
Consequently, a method and apparatus that has a reduced cost, that has mobility so that the sonar system may be transported with the ship as the ship changes locations, that can be configured for a desired perimeter typology, and that uses less power while providing a required degree of protection from underwater predators would be beneficial to advancing the art of diver sonar systems.
The present invention provides methods and apparatus for determining if an underwater intruder passes under a protective boundary in order to protect an asset such as a ship or a power plant. With an embodiment of the invention, a sonar sensor system comprises a plurality of sonar sensor modules that are spaced on a protective boundary. A sonar sensor module comprises a sonar transducer (sonar array) that is characterized by an omni-directional radiation pattern that may overlap an omni-directional radiation pattern of an adjacent sonar sensor module. The sonar sensor module may receive sonar signals from reflections off a target that may be an underwater intruder. The sonar sensor module collects sonar data such as range information of the target in relation to time. A central processor obtains the sonar data from each sonar module through a telemetry link. The central processor processes the sonar data from the plurality of sonar sensor modules in order to determine an estimated path of the target. Furthermore, the central processor may determine if the target should be considered as an underwater intruder from a threat level estimate such as a course direction, a target motion threat score, target echo width, or a target echo amplitude.
In a variation of the embodiment of the invention, the central processor determines the estimated path by matching sonar tracking data to different simulated sonar tracking data, in which each simulated sonar tracking data corresponds to a different simulated path of the target. In another variation of the embodiment, the central processor determines an initial estimated path from geometric parameters such as range differences and time differences that are obtained from adjacent sonar sensor modules. The central processor adjusts the estimated path in order to minimize an error function.